1. Field of the Invention
The present invention relates to an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill, the starting clutch being disposed in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism which receives an input of a power from the engine through a power transmission mechanism having built therein hydraulically operated frictional engaging elements.
2. Description of Related Art
In a vehicle having a function of stopping engine idling when the vehicle is at a standstill, at the time of vehicle start-up from the state of engine stopping, a hydraulic oil pressure in a hydraulic circuit becomes zero while the engine is stopped and a power transmission mechanism becomes an out-gear state (a state not fit for power transmission). Therefore, if the starting clutch is engaged earlier, when the power transmission mechanism has become an in-gear state (a state of being geared in), the power will be suddenly transmitted to driving wheels of the vehicle, resulting in shocks.
In order to avoid such disadvantages, the following is considered. Namely, a comparison is made between that rotational speed of the engine which serves as a rotational speed on an input side of the power transmission mechanism and that rotational speed of a drive pulley of the continuously variable transmission mechanism which serves as a rotational speed on an output side of the power transmission mechanism. When a deviation of the two rotational speeds has become smaller than a predetermined value so that a discrimination is made that the power transmission mechanism is in the in-gear state, the force of engagement of the starting clutch is increased.
In order to discriminate the in-gear state of the power transmission mechanism, it is considered to provide a rotational speed sensor for the engine aside from a rotational speed sensor for the drive pulley. This solution is, however, higher in cost. In this case, it is considered to input engine ignition pulses to an onboard (vehicle-mounted) computer so that the rotational speed of the engine can be calculated from the difference between the time of inputting an earlier inputted ignition pulse and the time of inputting the subsequently inputted ignition pulse. However, the ignition pulses of the engine are inputted only in number corresponding to the number of cylinders within two rotations of a crank shaft. At the time of rapid increase in rotation of the engine such as at the time of vehicle start-up from the state of engine stopping, that rotational speed of the engine which is calculated from the difference in time of in-putting the ignition pulses becomes considerably lower than the actual speed of rotation of the engine. Therefore, when the in-gear state of the power transmission mechanism is discriminated based on the deviation between that rotational speed of the drive pulley which is detected by the rotational speed sensor and that rotational speed of the engine which is calculated by the difference in time of inputting the ignition pulses, the discrimination of the in-gear state is delayed. A response to the vehicle stat-up, therefore, becomes poor.
In view of the above points, the present invention has an object of providing an apparatus for controlling a starting clutch in a vehicle having a function of stopping engine idling, wherein the in-gear state of the power transmission mechanism can be discriminated without delay without using a rotational speed sensor for the engine so that the vehicle start-up from the state of engine stopping can be made smoothly at a good response.
In order to attain the above and other objects, the present invention is an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill, the starting clutch being provided in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism which receives an input of a power from the engine through a power transmission mechanism having built therein hydraulically operated frictional engaging elements, wherein at a time of vehicle start-up from a state of engine stopping, control of the starting clutch is made based on a result of discrimination of discriminating means which discriminates as to whether the power transmission mechanism has become an in-gear state in which the power can be transmitted, the discriminating means being constituted such that, at the time of vehicle start-up from the state of engine stopping, a discrimination is made that the power transmission mechanism is in the in-gear state when a rotational speed of a drive pulley of the continuously variable transmission mechanism has increased to a predetermined speed.
At the time of vehicle start-up from the state of engine stopping, the drive pulley is stopped at the beginning of the vehicle start-up. As a result of engine starting, hydraulic oil pressure is supplied to hydraulically operated frictional engaging elements of the power transmission mechanism. When the power transmission through the power transmission mechanism has started, the drive pulley starts to rotate. Therefore, there is no problem even if the discrimination of the in-gear state is made based only on the rotational speed of the drive pulley. In a transmission in which a continuously variable transmission mechanism is built in, there has originally been provided rotational speed sensors which detect at a high accuracy the rotational speeds of the drive pulley and the driven pulley. The in-gear state of the power transmission mechanism can thus be judged without delay from the rotational speed of the drive pulley. Therefore, in case there is provided mode switching means which switches a control mode of the starting clutch, at a time when discriminating means discriminates that the power transmission mechanism has become the in-gear state, from a waiting mode in which an engaging force of the starting clutch is kept below a creeping force which generates a creeping of the vehicle to a running mode in which the engaging force of the starting clutch is increased above the creeping force, the discriminating means may be constituted as described hereinabove. Then, the control mode of the starting clutch can be switched to the running mode when the power transmission mechanism has actually become the in-gear state. The vehicle start-up from the state of engine stopping can thus be made smoothly at a good response.
In the embodiment to be described hereinafter, what corresponds to the above-described discriminating means is step S20 in FIG. 3. What corresponds to the above-described mode switching means is the processing from step S20 through S23 in FIG. 3.